Understanding the origin of the spin transition in LaCoO3 is one of the long- standing aims in condensed matter physics. Aside from its fundamental interest, a detailed description of this crossover will have a direct impact on the interpretation of the semiconductor-to-metal transition (SMT) and the properties of the high-temperature metallic phase in this compound, which has shown to have important applications in environmentally friendly energy production. To date, the spin transition has been investigated mainly as a function of temperature in thermal equilibrium. These results have hinted at dynamical effects. In this paper, we have investigated the SMT by means of pump-probe soft x-ray reflectivity experiments at the O K, Co L, and La M edges and theoretical calculations within a DFT++ formalism. The results point towards a laser-induced metallization in which the optical transitions stabilize a metallic state with high-spin configuration and increased charge disproportionation.
